A layer transfer sandblasting sleeve is a key tool in staged fracturing of vertical wells and horizontal wells in oil and gas fields. A sandblasting sleeve of this kind comprises an outer tube and a core tube disposed in the outer tube, wherein the outer tube and the core tube form a sliding fit. A wall of the outer tube of the sleeve is provided with a sandblasting hole, an upper end port of which has a sealed fitting surface for receiving a starting ball, which starts the sliding of the outer tube and the core tube of the sleeve. The size of the starting ball and that of the sealed fitting surface increase in accordance with a certain gradient sequence. Each starting ball has a diameter larger than the inner diameter of the fitting surface engaged with said starting ball, so that each starting ball can merely engage with a unique corresponding sealed fitting surface. During operation, corresponding starting balls are successively thrown down and a corresponding shear pin is sheared under the pressure built in the wellbore, so that the sleeve can be opened.
Currently, there are two steering fracturing methods for horizontal and vertical oil and natural gas wells, i.e., limited entry fracturing and staged fracturing. Staged fracturing is the dominating method, including chemical staged fracturing, packer staged fracturing, hydraulic staged fracturing, coiled tubing staged fracturing and combined completion, among which the most widely used is packer staged fracturing, including pumping bridge plug staged fracturing, ball and sleeve packer segment, annular packer and double sealed single pressure staged fracturing, etc.
Among the above methods, annular packer and the pumping bridge plug staged fracturing methods have no limitation on the number of stages. The fracturing operations thereof, however, cannot be continuously performed. Re-perforation is required after the operation is completed in each stage. After the operations are completed, well killing and plug drilling are needed, which result in long periods of operations and high costs. In double sealed single pressure staged fracturing, the casing string needs to be dragged, and the packer requires multiple sealing, whereby the construction period is prolonged. Ball and sleeve packer staged fracturing use a combination of balls and ball seats of different size ranges, so that multi-stage fracturing can be accomplished without operating the casing string. However, because different balls are designed in accordance with a certain size range, the number of packer stages is limited by the size of the casing string, and staged fracturing and acidification series will also be restricted.
In recent years, different sandblasting sleeves for different reservoir characteristics have been successively developed. For example, CN 210048U entitled “Pressure guide sandblasting sleeve for fracturing”, which was issued on Apr. 1, 1992, discloses a device mainly used in oil well fracturing. And a device mainly used in gas well fracturing is disclosed in CN 200820061922 entitled “Sandblaster of fracturing sleeve”, which was on Nov. 5, 2008. Both of the sleeves as disclosed above are based on the principle of opening sleeves with starting balls, the size of which increases in sequence, whereby the number of staged fracturing is still limited.
In addition, in order to overcome the defects of fracturing devices, a variety of sleeve fracturing devices also have been developed. For example, in CN201396131 entitled “Horizontal well mechanical staged fracturing blocking-proof process pipe column” which was published on Feb. 3, 2010, it discloses a device comprising a tubing string, a pressure differential packer, a safety connector and a slide sleeve packer. The pressure differential packer and the slide sleeve packer are mounted on the tubing string with the safety connector arranged therebetween. This device can only be applied in oil fields, and the packers thereof can be easily damaged during operations, rendering loose sealing and inadequate fracturing. Further, this device is of complex and labor-intensive operations with poor security.
In CN101338663 entitled “Staged fracturing horizontal wells mechanical anti-card technology column”, which was published on Jan. 7, 2009, it discloses a device comprising an oil pipe, a safe joint, a centralizer, a hydraulic anchor, a packer, a pressure guide sandblaster and a guide plug, wherein, the lower end of the oil pipe is successively connected with the safe joint, the centralizer, the hydraulic anchor, the packer, the centralizer, the pressure guide sandblaster, the packer and the guide plug. This device can only be used for horizontal well oilfield fracturing, but cannot achieve multi layer fracturing and mining without operating the string, nor can it achieve staged fracturing without operating the string or limiting the number of stages.
In CN101560877 entitled “Horizontal well packer staged fracturing technology tube pillar” which was published on Oct. 21, 2009, it discloses a device comprising an oil string, a hydraulic anchor, a seat sealing controller, a straddle packer A, a straddle packer B, a straddle packer C, a sleeve sandblaster, a sandblaster, a guider and a capillary tube. The oil string is successively provided with the hydraulic anchor, the seat sealing controller, the straddle packer A, the sleeve sandblaster, the straddle packer B, the sandblaster, the straddle packer C and the guider. The capillary tube connects to the seat sealing controller, the straddle packer A, the straddle packer B and the straddle packer C on one side of the oil string. This device, however, cannot achieve unlimited number of staged fracturing.
Moreover, CN101418681 entitled “Once tubular column process for combination oil production by multiple fracturing for oil and gas wells”, and CN201144682 entitled “Multiple fracturing pipe column for petroleum and gas wells” both adopt a method of opening the sleeves by throwing balls, wherein unlimited numbers of staged fracturing without operating the column string is impossible, nor can the sleeve be closed.
Therefore, a fracturing device that can open or close any sleeve as required is urgently needed for achieving staged fracturing with unlimited numbers of stages in horizontal, vertical and directional wells without having to operate the tabular column.